**4.3.2 Scenario II – 500 kWel CHP unit**

184 Biogas

To prove plausibility of the optimum PNS structure two scenarios were carried out, both for minimum as well as for maximum substrate cost situations. In the first case the maximum structure was reduced by taking away corn availability. With that only five substrate mixtures could be used for biogas production. The second scenario was set up to get an idea how feedin tariffs can influence the outcome of an optimization. Therefore it was not allowed that a

As already mentioned in the beginning corn is currently a dominating substrate for biogas production. To show the potential of intercrops no corn is available in this scenario. Not to lose the comparability the amount of corn was compensated with an additional availability of intercrops. The calculation was based on the CH4-outputs and adds up to additionally 904 t intercrops. With that 2,170 t/yr intercrops, about 1.7 times more than in the basic maximum structure shown in Figure 2, are available in the maximum structure of this scenario. Under these conditions PNS could choose between five different substrate feeds. The optimization results in a technology network including two locations using the whole

network set-up results e.g. in two 250 kWel CHPs if a 500 kWel instead could be taken.

Fig. 4. PNS optimum structure for scenario 1 without corn silage availability

At location 3 a fermenter processing substrate feed 7 with a capacity to produce biogas to supply a 250 kWel CHP runs 7,800 full load hours a year. A second fermenter placed on

**4.3 Scenarios** 

**4.3.1 Scenario I – No corn silage** 

amount of available intercrops as shown in Figure 4.

Operating a 500 kWel CHP goes along with reduced feed-in tariffs of 20 €/MWh according to Austrian's Eco-Electricity Act. The positive effect of lower investment and operating costs for larger capacities is therefore narrowed by less revenue for produced electricity. If is forbidden to use two CHPs with same capacity at one location in the maximum structure to gain higher feed-in tariffs the next larger CHP capacity has to be taken although this would

Fig. 5. PNS optimum structure with a central 500 kWel CHP

region.

the solutions presented is recommended.

+ self-loading trailer from Table 4 was used.

Table 10. LCIA results based on PNS scenarios

solution because of two small CHP units instead one.

**5. SPI evaluation** 

valued product.

Economic and Ecological Potential Assessment for Biogas Production Based on Intercrops 187

the best revenue, because of higher plant utilization and higher revenue for electricity and heat production. Although in the optimal scenario the amount of corn relating to the total feedstock was not even 17 % of the total (dry matter) the compensation for corn with intercrops results in higher revenue. For more corn that intercrops compensate in the input the impact would be even higher. Therefore it is obvious that intercrops can be a profitable feedstock to run a biogas plant. For the case study the availability of intercrops would have to be raised as described before which would lead to the best technology network for the

The system has two limiting factors; on the one hand the distances between the fermenter locations and the feedstock providers accompanying different transport costs and on the other hand the limited resource availability. It could be shown that it is not lucrative to run a central CHP with higher capacity (500 kWel) as feed-in tariffs are lower and less revenue can be gained. Nevertheless, from the point of view of sustainability, it would be preferable to substitute two smaller CHPs with a bigger one. An adaptation of reimbursement schemes to

Based on the economic results of the PNS optimization and previous SPI evaluation of different intercrops, a footprint for the PNS results was calculated. The evaluation includes every substrate, transport, net electricity and infrastructure for fermenters and CHP units. SPIonExcel already provides a huge database of LCIA datasets which can be used for modeling the scenarios. In case of intercrops substrate the SPI value for conservation tillage

**Optimum solution** 93.08 3,825 21,503 4,591 2,360 **Scenario 1 - No corn** 89.32 3,900 20,236 4,680 2,221 **Scenario 2 - 500KWel BHKW** 91.51 3,825 20,876 4,591 2,539

The overall footprint points out the environmental impact for one year of production. In case of the optimum solution it would need 93.08 km² of area which has to be reserved to embed the production sustainably into nature. The overall footprint is shared between both products according the amount of output and the price per MWh (electricity: 205 €/MWh; heat: 22.5 €/MWh). Price allocation of the footprint leads to a higher footprint for the higher

Scenario 1 has a benefit from the ecological point of view and almost equal revenue according to Table 9. For scenario 2 there is only a slightly difference to the optimum

Main impact categories are in every case 'fossil carbon', 'emissions to water' and 'air'. This mainly derives from the utilization of net electricity which contributes around 45 % to the whole footprint. Main contribution to this categories stemming from net electricity and

**electricity SPI evaluation results** 

**overall SPI [km²] production [MWh / a] SPI [m² / MWh] production [MWh / a] SPI [m² / MWh]**

**heat**

go along with shortened revenue. With this precondition the optimization of the maximum structure presented in Figure 2 but with only one central 500 kWel CHP unit whereas the rest of the optimum structure (Figure 3) stays the same.

The revenue is narrowed but not as much as it was in scenario 1. To use a 500 kWel central CHP would cause a revenue reduction of yearly 50,000 € within a payout period of 15 years.
